This invention relates to a nozzle apparatus that utilizes laser energy and powdered metal for correcting surface defects in metal articles and, more particularly, relates to apparatus which is an improvement of that disclosed in U.S. Pat. No. 4,724,299 issued Feb. 9, 1988 to A. W. Hammeke for LASER SPRAYING NOZZLE AND METHOD.
The apparatus disclosed in U.S. Pat. No. 4,724,299 is a torch nozzle that sprays metal powder into a shallow puddle of molten metal formed on the surface of a workpiece by a laser beam. Normally, the laser beam is directed inside the torch, and is focused to contact the metal powder at or near the surface of the workpiece. The latter is positioned in close proximity to the outlet of the spray nozzle and because of this the nozzle is subjected to a high level of heat which radiates from the of workpiece region that is melted by the laser beam. This radiant energy heats the spray nozzle to such an extent that it must be replaced frequently, and it must also be serviced frequently because molten material that sputters from the surface of the workpiece tends to clog or partially block the nozzle outlet. Further, spray nozzles constructed according to the teachings of U.S. Pat. No. 4,724,299 tend to be unduly bulky thereby preventing utilization thereof for cladding in cramped work locations. In addition, while inert gas that flows with the powdered metal through the same outlet as the laser beam provides an oxidation seal, such seal is not sufficient to assure that the weld-like repairs which are produced will, on a consistent basis, be clean (i.e. free of oxidation and/or other contaminants).
The prior art, as depicted in FIG. 15 hereof, has attempted to avoid the above noted problems of weld oxidation and frequency of nozzle repair by providing a flow of inert cooling gas that is directed along the outside surface of the nozzle tip and toward the surface being repaired. More particularly, a laser beam produced by source 21 is directed downward through focusing lens 22, exit 256 at the front of longitudinal passage 219 for rear unit 211, and exit 223 at the front of front unit 215, being focused at upper surface 24 of workpiece 25 to create shallow puddle 26 of molten metal. At the same time, metal powder carried by an inert gas flows downward in conical passage 235 between the outside of rear unit 211 and the inside of front unit 215, and through exit 223 into puddle 26.
The front portion of nozzle apparatus 200 is subjected to very high temperatures radiated from surface 24. To cool apparatus 200 water or other cooling fluid is circulated in jacket 240 that is formed between inner and outer cups 216, 217 of front unit 215. Increased cooling and shielding is obtained by providing a substantial flow of inert gas directed into manifold 275 that is formed by annular jacket 219 which surrounds front unit 215 and is located a substantial distance behind work surface 24. This inert cooling gas exits manifold 275 through the screened lower surface 220 of jacket 219 that defines manifold 275, and flows along the outside of front unit 215 to impinge upon surface 24.
While the flow of inert gas from manifold 275 provides increased cooling and increases shielding of metal in puddle 26 from oxidation, the construction of jacket 219 creates problems of its own. That is, jacket 219 makes the tip of apparatus 200 too bulky to fit into confined areas. Further, the large horizontal area provided by screened surface 220 absorbs more radiant heat as compared to a steeply inclined surface that tends to reflect much of the radiant heat away from the source radiating same. Further, since exit screen 220 of jacket 219 is a substantial distance from exit 223 at the front of nozzle 218 inert cooling gas from manifold 275 has only a limited cooling effect on tip 218, has only a limited effect on preventing oxidation from occurring at the repair or weld site (puddle 26), and has only a limited effect in driving sputtering particles back to the puddle 26 of molten metal from whence they came.